Need some help with Testing silver

Questions on polishing, restoration, conservation + manufacturing techniques
zeeborg
Posts: 3
Joined: Mon Jan 19, 2009 10:03 pm

Need some help with Testing silver

Postby zeeborg » Wed May 18, 2016 12:18 pm

I picked up a couple of very old candlesticks last week.
They were in very poor condition. I got them cheap at a thrift store, so figured what the heck.
I'm going to scrap them if they have silver content to help fund my collection.

I just got a fresh order of JSP silver and gold testing acid, and tried it.
Typically, when you put acid on base metals, they turn a green or bluish color (like the watch case pictures attached)
When I apply the silver test to the tarnished part (I believe is plate) it shows red flakes.
When I apply the gold test, NO reaction.
When I scrape a section off to clean it to fresh metal:
the silver test gives a whitish/gray residue and leaves a black mark.
the gold test creates a creamy light gray lump, and blackens the metal. (I've read that the creamy lump is silver nitrate?)
If I use acid on the shavings, they react violently, and give off a mustard colored smoke and then leaves a light gray 'ash'.

This has me very stumped.
I've done some searching, and best guess is some kind of silver alloy 'coin silver' material less than 80& silver?

Your thoughts?

I have photos, but no way to link them, as they are on my computer with no way to host them.

AG2012
contributor
Posts: 3642
Joined: Fri Apr 13, 2012 9:47 am

Re: Need some help with Testing silver

Postby AG2012 » Wed May 18, 2016 2:23 pm

Hi,
First of all, why gold test on silver? Forget gold testing acids, they are used to determine Karats on black stone plate.
Find an inconspicuous place on the item and make a small scratch. This is necessary to get to the underlying metal. Scratch the piece using a jeweler`s metal file.
Then apply small drop of testing acid; its principal component is chromic acid. Chemical reaction is the precipitation of silver chromate (Ag2CrO4) of red color; the more silver the more intensive (bright) red. The reaction occurs within a second.
When this chemical reaction is understood it is much easier to proceed with testing. There is no miraculous color change (confusing different shades of red, brown, yellow green etc. described elsewhere). Actually we look for precipitated silver salt which is RED. Lower fineness will give less bright red because there is less silver to react with. Base metals will give no red color because there is no silver in them and will turn green or dull yellow. Make sure to clean silver dust after filing; the test is very sensitive and tiny particles of silver dust may react with chromic acid.
I have to use jeweler`s 10 x loupe when testing, but I suppose your eyesight is better than mine.
In a word, red color tells it`s solid silver, not plate.
Acid testing is more or less a qualitative test (it will tell if the alloy has silver, not meant to determine the exact fineness).
Best wishes

AG2012
contributor
Posts: 3642
Joined: Fri Apr 13, 2012 9:47 am

Re: Need some help with Testing silver

Postby AG2012 » Tue May 24, 2016 5:51 am

Hi,
The lowest fineness of .750 (12 Loth) often used in Prussia, when tested, will also precipitate silver chromate (Ag2CrO4), sometimes barely visible with naked eye, but it`s there, proving silver alloy.
Another tip: after filing, the surface may not react as expected, leading to wrong conclusion it`s not a silver alloy. The test should be repeated; just wipe off using a cotton rag and apply another drop – red color will appear.
Sterling is not the problem, lower fineness, especially lower than .750 may be tricky. Do not underestimate low fineness – many beautiful items were made of .500 in e.g. Ottoman Empire, not well legislated and without any marks. Just look for precipitated red silver chromate (tiny red flakes within yellow- greenish liquid of the applied drop).
Again, it`s a qualitative test, more or less, although intensive, vivid red indicates high silver contents in the alloy.
Best wishes


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